Preparation of Pt/ZSM-5 films on stainless steel microreactors

Engineering of zeolite BEA crystal size and morphology via seed-directed steam assisted conversion

The mechanism of seeding of zeolite BEA via steam assisted conversion has been studied using BEA seeds with different composition. The catalysts are characterized by X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption-desorption, Hg-porosimetry, X-ray fluorescence and TPD of ammonia, and evaluated in benzene alkylation with propene. The results show that variation of the SiO₂/Al₂O₃ ratio from 25 to 250 in BEA seeds changes the mechanism of seeding from "core-shell" to a "dissolution" mechanism, which can serve as a tool for engineering the morphological, textural and catalytic properties of BEA zeolites. Al-rich seeds (SiO₂/Al₂O₃ = 25) do not dissolve during gel preparation and initiate dense oriented crystal growth on their surface resulting in the formation of large polycrystals (1-2 μm) with ordered densely intergrown nanocrystallites. In contrast, Si-rich seeds (SiO₂/Al₂O₃ = 250) dissolve into tiny fragments, which serve as individual nuclei leading to formation of tiny isolated nanocrystallites aggregated into small hierarchical aggregates with high intercrystalline mesoporosity. The decrease of particle size and formation of intercrystalline mesoporosity in hierarchical aggregates improves the accessibility of acidic sites and facilitates the diffusion of reaction products, which leads to the significant improvement of catalytic activity and reduces the deactivation resulting in higher stability with time on stream in cumene synthesis from benzene and propylene.

Monolithically Integrated Diffused Silicon Two-Zone Heaters for Silicon-Pyrex Glass Microreactors for Production of Nanoparticles: Heat Exchange Aspects

We present the design, simulation, fabrication and characterization of monolithically integrated high resistivity p-type boron-diffused silicon two-zone heaters in a model high temperature microreactor intended for nanoparticle fabrication. We used a finite element method for simulations of the heaters’ operation and performance. Our experimental model reactor structure consisted of a silicon wafer anodically bonded to a Pyrex glass wafer with an isotropically etched serpentine microchannels network. We fabricated two separate spiral heaters with different temperatures, mutually thermally isolated by barrier apertures etched throughout the silicon wafer. The heaters were characterized by electric measurements and by infrared thermal vision. The obtained results show that our proposed procedure for the heater fabrication is robust, stable and controllable, with a decreased sensitivity to random variations of fabrication process parameters. Compared to metallic or polysilicon heaters typically integrated into microreactors, our approach offers improved control over heater characteristics through adjustment of the Boron doping level and profile. Our microreactor is intended to produce titanium dioxide nanoparticles, but it could be also used to fabricate nanoparticles in different materials as well, with various parameters and geometries. Our method can be generally applied to other high-temperature microsystems.

Recent advances in preparation methods for catalytic thin films and coatings

Advancements in the preparation methods and applications of catalytic thin films and coatings are briefly summarized.

Chemistry in supercritical fluids for the synthesis of metal nanomaterials

The supercritical flow synthesis of metal nanomaterials is sustainable and scalable for the efficient production of materials.